Blood in Faeces

blood in the faeces

The term rectal bleeding is often used by doctors to mean any blood that is passed out when you go to the toilet to pass faeces. However, not all bleeding that is passed out actually comes from the rectum. The blood can come from anywhere in the gut .

What is the gut?

  • The gut (gastrointestinal tract) starts at the mouth and ends at the anus. When we eat or drink, the food and liquid travel down the oesophagus  into the stomach. The stomach churns up the food and then passes it into the small intestine.
  • The small intestine (sometimes called the small bowel) is several metres long and is where food is digested and absorbed.
  • Undigested food, water and waste products are then passed into the large intestine (sometimes called the large bowel). The main part of the large intestine is called the colon, which is about 150 cm long. This is split into four sections: the ascending, transverse, descending and sigmoid colon. Some water and salts are absorbed into the body from the colon.
  • The colon leads into the rectum (back passage) which is about 15 cm long. The rectum stores faeces (stools) before they are passed out from the anus.

Severity of the bleeding

Bleeding can range from a mild trickle to a massive life-threatening severe bleed (a severe haemorrhage). There is no immediate risk to life with mild, intermittent GI bleeding. Sometimes bleeding from a condition in the gut is so mild (like a slight trickle) that you do not notice any actual bleeding and it is not enough to change the colour of your faeces. However, a test of your faeces can detect even small amounts of blood.

Site of the bleeding

Bleeding from the anus or low down in the rectum - the blood tends to be bright red and fresh. It may not be mixed in with faeces but instead you may notice blood after passing faeces, or streaks of blood covering faeces. For example, bleeding from an anal fissure or from haemorrhoids (described later).

Bleeding from the colon - often the blood is mixed up with faeces (motions or stools). The blood may be a darker red. For example, bleeding from colitis, diverticula disease, or from a bowel tumour.

Bleeding from the stomach or small intestine - the blood has far to travel along the gut before it is passed out. During the time it takes to do this the blood becomes altered and dark and mixes with faeces. This can make your faeces turn a black and tarry- this is called melaena. For example, this may occur due to a bleeding stomach or duodenal ulcer.

What are the causes of rectal bleeding / GI tract bleeding?

Haemorrhoids (piles)

There is a network of small veins within the inside lining of the anus and lower rectum. These veins sometimes become wider and engorged with more blood than usual. These engorged veins and the overlying tissue may then form into one or more small swellings called haemorrhoids. The most common symptom is bleeding after going to the toilet.

Anal fissure

An anal fissure is a small tear of the skin of the anus. Although the tear is usually small, it can be very painful because the anus is very sensitive. Often an anal fissure will bleed a little. The blood is usually bright red and stains the toilet tissue, but soon stops.


A diverticulum is a small pouch with a narrow neck that sticks out from the wall of the gut. Diverticula means more than one diverticulum. They usually occur in the colon. A diverticulum may occasionally bleed and you may pass some blood via your anus. The bleeding is due to a burst blood vessel that sometimes occurs in the wall of a diverticulum and so the amount of blood loss can be heavy.

Crohn's disease

Crohn's disease is a condition which causes inflammation in the gut. The disease flares up from time to time. Common symptoms include bloody diarrhoea, abdominal pain, and feeling unwell.

Ulcerative colitis

Ulcerative colitis (UC) is a disease where inflammation develops in the colon and rectum. A common symptom when the disease flares up is diarrhoea mixed with blood. The blood comes from ulcers that develop on the inner wall of the inflamed gut.


A bowel polyp (adenoma) is a small growth that sometimes forms on the inside lining of the colon or rectum. Most develop in older people. Polyps are benign (non-cancerous) and usually cause no problems. However, sometimes a polyp bleeds and sometimes a polyp can turn cancerous.


Cancer of the colon and rectum are common cancers in older people. Rectal bleeding is one symptom that may occur. Bleeding is often not obvious and other symptoms are often present before visible bleeding occurs. For example, pains, anaemia, weight loss, diarrhoea or constipation.


Angiodysplasia is a condition where you develop a number of enlarged blood vessels within the inner lining of the colon. The cause is unknown, but they occur most commonly in older people. Bleeding from an angiodysplasia is painless. The blood seen can range from bright red brisk bleeding, to dark blood mixed with faeces, to melaena.

Stomach and duodenal ulcers

An ulcer in the stomach or duodenum may bleed. This can cause melaena - where your faeces turn black as described earlier.

Some gut infections

May cause bloody diarrhoea due to inflammation of the gut, caused by some infections.

What should you do?

If the bleeding is heavy, or if you have melaena, see a doctor immediately or call an ambulance. If you feel dizzy, collapse or feel generally unwell then consider calling an ambulance, as this might indicate a heavy bleed.

Some people assume that their rectal bleeding is due to haemorrhoids (piles) and do not get it checked out. Haemorrhoids are perhaps the most common cause of rectal bleeding. However it is dangerous to make assumptions.

What tests might be advised?

Two of the most common tests done when someone has rectal bleeding are called colonoscopy and sigmoidoscopy.

What is a colonoscopy?

A colonoscope is a thin, flexible telescope. It is about as thick as a little finger. It is passed through the anus and into the colon. It can be pushed all the way round the colon as far as the caecum (where the small and large intestine meet).

The colonoscope contains fibre optic channels which allow light to shine down so the doctor can see inside your colon. This is done either by looking down the colonoscope, or by attaching the colonoscope to a TV monitor.

The colonoscope also has a side channel down which devices can pass. The doctormay take a small sample (biopsy) from the inside lining of the colon by using a thin grabbing instrument which is passed down a side channel.

What is a sigmoidoscopy?

The sigmoid colon is the final portion of the bowel that is joined to the rectum. A sigmoidoscope is like a small telescope with an attached light source about the thickness of your finger. It is similar to a colonoscope but much shorter. A sigmoidoscopy is easier to do than a colonoscopy. A doctor inserts the sigmoidoscope into the anus and pushes it slowly into the rectum and sigmoid colon. This allows the doctor to see the lining of the rectum and sigmoid colon.

What is a faecal occult blood test?

The fecal occult blood test (FOB test) detects small amounts of blood in your feces which you would not normally see or be aware of.

When and why is the fecal occult blood test done?

If you only have a small amount of blood in your feces then the feces look normal. However, the FOB test will detect the blood. So, the test may be done if you have other symptoms that may suggest a gut problem. It may also be done to screen for bowel cancer before any symptoms develop.

How is the fecal occult blood test done?

A small sample of feces is smeared on to a piece of card. The sample is tested by adding a chemical to the sample on the card. If there is a change in color after adding the chemical, it indicates that some blood is present.

Sometimes two or three FOB tests are done on two or three separate samples of feces, obtained on different days. This is because a bleeding disorder of the gut may only bleed now and then.

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